IMS network access using legacy devices

ABSTRACT

A communication network is described that allows legacy devices to access an IMS network. The communication network includes a switching system, an IMS network, and a non-IMS network. The switching system includes a subscriber database that is pre-provisioned with identities of IMS subscribers using legacy devices. When in operation, a calling party places a call through a legacy device. The switching system receives the call and accesses the subscriber database based on a calling party identifier (e.g., a phone number, URL, etc) to determine if the calling party is an IMS subscriber. If the calling party is an IMS subscriber, then the switching system routes the call to the IMS network. If the calling party is not an IMS subscriber, then the switching system routes the call to the non-IMS network.

RELATED APPLICATIONS

This patent application claims priority to a foreign patent applicationfiled in the Chinese Patent Office, having the application number200510054440.6 and filed on Mar. 10, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is related to the field of communications, and inparticular, to providing access to IMS networks and IMS services usinglegacy devices.

2. Statement of the Problem

As set forth in the 3^(rd) Generation Partnership Project (3GPP), an IPMultimedia Subsystem (IMS) provides a common core network havingaccess-agnostic network architecture for converged networks. Serviceproviders are accepting this architecture in next generation networkevolution. The IMS architecture is initially defined by the 3GPP toprovide multimedia services to mobile subscribers over an IP network. IPnetworks have become the most cost savings bearer network to transmitvideo, voice, and data. IMS uses the advantage of IP networks to providemultimedia services for IMS subscribers on an IMS platform. Thesignaling used within IMS networks is SIP protocol. IMS defines thestandard SIP interface between application servers, the IMS core network(CSCF), the IMS subscriber, the IMS database (HSS), and IMS billingelements. These standards can reduce the network integration costs andlet the subscriber enjoy more stable services.

On the IMS platform, the traditional supplementary services, such ascall forwarding, conferencing, and call waiting could be available forIMS subscribers. Also, many new data services, such as instantmessaging, video calls, video on wait, and web-based services, will alsobe available for the IMS subscribers.

An IMS subscriber uses an IMS device to access the IMS network and itsassociated IMS services over the IP network. Before the IMS services areavailable to the IMS subscriber, the IMS subscriber needs to registerwith the IMS network through the IMS device. The registration providesmany functions in the IMS network, such as authenticating thesubscriber, determining the services available to the subscriber, etc.The registration procedure is according to IMS standards. Thus,IMS-compliant devices are able to register with the IMS network toreceive IMS services.

One problem with IMS networks as currently defined by the 3GPP is thatlegacy devices, such as traditional telephones, that do not registerwith the IMS networks are not able to access the IMS networks and IMSservices. There are many legacy devices being used for communicationthat are not able to register with an IMS network. One type of legacydevice is an H.323 IP device. H.323 IP devices do perform someregistration when accessing a network, but the registration is notcompliant with IMS standards. Another type of legacy device is atraditional telephone using the Public Switched Telephone Network(PSTN). Traditional phones are circuit-based and do not register with anetwork before use. There is currently no effective way for legacydevices to register with and access IMS networks and IMS services.

SUMMARY OF THE SOLUTION

The invention solves the above and other related problems by providingaccess to IMS networks using legacy devices. The inventionadvantageously allows IMS subscribers to use legacy devices to accessIMS services, without the legacy devices having to perform IMSregistration. IMS subscribers are not limited to mobile devices asdefined by the 3GPP, but may use mobile devices, wire line devices, orany other legacy devices. Because many or most communication devicescurrently used are legacy devices, service providers will be able tooffer IMS services to many more potential subscribers. Also, users thatare comfortable with traditional telephones will have access to IMSservices without having to use an IMS-compatible device, and will stillbe able to access to the traditional services.

One embodiment of the invention comprises a communication network thatallows legacy devices access to an IMS network. The communicationnetwork includes a switching system, an IMS network, and a non-IMSnetwork. The legacy device comprises any device not able to registerwith the IMS network. The legacy device allows a calling party to placea call over the communication network. The switching system includes asubscriber database that is pre-provisioned with identities of IMSsubscribers using legacy devices in the communication network.

When in operation, a calling party places a call through the legacydevice. The switching system receives the call from the legacy device.The call includes a calling party identifier that identifies the callingparty. For instance, in a circuit-based call, the calling partyidentifier may comprise a telephone number that is included in thesignaling (SS7, ISDN, etc) for the call. For a packet-based call, thecalling party identifier may comprise a static IP address or a URL thatis included in a header of the packets for the call. The switchingsystem accesses the subscriber database based on the calling partyidentifier to determine if the calling party is an IMS subscriber. Ifthe calling party is an IMS subscriber, then the switching system routesthe call to the IMS network. If the calling party is not an IMSsubscriber, then the switching system routes the call to the non-IMSnetwork.

The invention may include other exemplary embodiments described below.

DESCRIPTION OF THE DRAWINGS

The same reference number represents the same element on all drawings.

FIG. 1 illustrates a communication network in an exemplary embodiment ofthe invention.

FIG. 2 illustrates a switching system in an exemplary embodiment of theinvention.

FIG. 3 is a flow chart illustrating a method of operating thecommunication network of FIG. 1 in an exemplary embodiment of theinvention.

FIG. 4 is a flow chart illustrating a method of routing a call from theswitching system to the IMS network in FIG. 1 in an exemplary embodimentof the invention.

FIGS. 5-9 illustrate call flows through a communication network inexemplary embodiments of the invention.

FIG. 10 illustrates another switching system in an exemplary embodimentof the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-10 and the following description depict specific exemplaryembodiments of the invention to teach those skilled in the art how tomake and use the best mode of the invention. For the purpose of teachinginventive principles, some conventional aspects of the invention havebeen simplified or omitted. Those skilled in the art will appreciatevariations from these embodiments that fall within the scope of theinvention. Those skilled in the art will appreciate that the featuresdescribed below can be combined in various ways to form multiplevariations of the invention. As a result, the invention is not limitedto the specific embodiments described below, but only by the claims andtheir equivalents.

FIG. 1 illustrates a communication network 100 in an exemplaryembodiment of the invention. Communication network 100 includes aswitching system 104, an IMS network 108, and a non-IMS network 110.Legacy device 102 accesses communication network 100 through switchingsystem 104. Switching system 104 connects to IMS network 108, andnon-IMS network 110. Switching system 104 includes a subscriber database106 in this embodiment. Alternatively, subscriber database 106 may beremote from switching system 104 and accessible by switching system 104over a network. Communication network 100 may include other devices,systems, or networks not shown in FIG. 1.

Legacy device 102 comprises any communication device that does notregister with an IMS network. IMS-compliant devices as defined by the3GPP are mobile devices that register with the IMS network. Legacydevices as defined herein are not IMS-compliant devices. Legacy devicesmay be mobile (or wireless) devices, or wire line devices (circuit-basedor packet-based). One example of a legacy device 102 is a traditionaltelephone that communicates with a circuit-based network. A traditionaltelephone initiates a call with call signaling, such as SS7 signaling,ISDN signaling, etc. The traditional telephone does not register withthe circuit-based network prior to placing a call, so it is not equippedor compatible to register with an IMS network. Another example of alegacy device 102 is a packet-based phone that does not register with anIMS network. Packet-based phones, such as VoIP phones using H.323protocol, do register with networks, but the registration is notcompliant with IMS standards.

To “register” with an IMS network means an IMS subscriber has a devicethat supports IMS-compliant SIP protocol that is used to register withthe IMS network and service control. In the registration process, theIMS device transmits a SIP Register message to its related IMS CallSession Control Function (CSCF) element. The CSCF element queries theHome Subscriber Server (HSS) database to retrieve, check, and update thesubscriber's registration information. The CSCF then downloads theservice profile of the IMS subscriber. The IMS subscriber can use theIMS service anytime and anywhere. Each registration will have a limitedtime period. If the time period expires, the IMS subscriber needs tore-register to IMS network.

An IMS network 108 comprises any network that provides IMS services. AnIMS network 108 may be defined by the 3GPP or any subsequent standardsbody. A non-IMS network 110 comprises any network that is not consideredan IMS network. For instance, a non-IMS network 110 may comprise apublic-switched telephone network (PSTN) or an IP network not providingIMS services.

FIG. 2 illustrates switching system 104 in an exemplary embodiment ofthe invention. Switching system 104 includes subscriber database 106, anoriginating interface 202, a processing system 204, and a terminatinginterface 206. Processing system 204 is connected to originatinginterface 202, terminating interface 206, and subscriber database 106.Originating interface 202 is operable to communicate with legacy device102 (see FIG. 1). Terminating interface 206 is operable to communicatewith IMS network 108 and non-IMS network 110 (see FIG. 1). Switchingsystem 104 may comprise a soft switch, such as the Lucent Softswitch(LSS).

Processing system 204 may execute instructions that are stored onstorage media (not shown) to perform the operations of switching system104. The instructions can be retrieved and executed by processing system204. Some examples of instructions are software, program code, andfirmware. Some examples of storage media are memory devices, tape,disks, integrated circuits, and servers. The instructions areoperational when executed by processing system 204 to direct processingsystem 204 to operate in accord with the invention. The term “processingsystem” refers to a single processing device or a group ofinter-operational processing devices. Some examples of processors arecomputers, integrated circuits, and logic circuitry.

In FIG. 1, calling party 101 is using legacy device 102 to place a call.Although legacy device 102 does not register with IMS network 108,communication network 100 allows calling party 101 to access IMS network108 and the IMS services according to the following method.

FIG. 3 is a flow chart illustrating a method 300 of operatingcommunication network 100 of FIG. 1 in an exemplary embodiment of theinvention. In step 302, subscriber database 106 is pre-provisioned withidentities of IMS subscribers using legacy devices. Prior to placingcalls, calling party 101 contacts a service provider and subscribes toIMS services offered by the service provider. The service providerpre-provisions subscriber database 106 and any other applicablesubscriber databases. Subscriber database 106 stores the identities ofIMS subscribers using legacy devices, including the identity of callingparty 101. The identities of the IMS subscribers using legacy devicesmay comprise phone numbers (E164 numbers), IP addresses, URLs, or anyother identifier for the IMS subscribers.

In step 304, switching system 104 receives a call from calling party 101using legacy device 102. The call includes a calling party identifierthat identifies calling party 101. For instance, in a circuit-basedcall, the calling party identifier may comprise a telephone number thatis included in the signaling (SS7, ISDN, etc) for the call. For apacket-based call, the calling party identifier may comprise a static EPaddress or a URL that is included in a header of the packets for thecall.

In step 306, switching system 104 accesses subscriber database 106 basedon the calling party identifier to determine if calling party 101 is anIMS subscriber. Subscriber database 106 may be indexed with callingparty identifiers for all of the IMS subscribers of the service providerthat may be using legacy devices to access IMS network 108. Switchingsystem 104 may enter the calling party identifier into subscriberdatabase 106 to yield an indicator as to whether calling party 101 is anIMS subscriber. The indicator may be a true/false, a yes/no, or someother indicator.

If calling party 101 is an IMS subscriber, then switching system 104routes the call to IMS network 108 in step 308. If calling party 101 isnot an IMS subscriber, then switching system 104 routes the call tonon-IMS network 110 in step 310.

FIG. 4 is a flow chart illustrating a method 400 of routing a call fromswitching system 104 to IMS network 108 in FIG. 1 in an exemplaryembodiment of the invention. In step 402, switching system 104 generatesa packet signaling message for the call. For instance, if switchingsystem 104 uses SIP to communicate with IMS network 108, then switchingsystem 104 generates a SIP INVITE message for the call. In step 404,switching system 104 includes or inserts an indicator in a header of thepacket signaling message that calling party 101 is an IMS subscriber.Assume again that SIP is being used. Switching system 104 may include anindicator in the header of the SIP INVITE message that the call isoriginated by an IMS subscriber using a legacy device. The indicator maybe inserted in an existing field of the header of the SIP INVITEmessage, or a new field may be designated for the indicator. In step406, with the packet signaling message formatted, switching system 104transmits the packet signaling message to IMS network 108. IMS network108 may then process the packet signaling message. IMS network 108 mayprocess the indicator in the header of the packet signaling message toidentify a service profile for calling party 101. IMS network 108 mayprocess the indicator in the header of the packet signaling message toidentify a serving-call session control function (S-CSCF) for the call.

Communication network 100 advantageously allows IMS subscribers to uselegacy devices to access IMS networks, without the legacy devices havingto perform IMS registration. IMS subscribers are not limited to mobiledevices as defined by the 3GPP, but may use mobile devices, wire linedevices, or any other legacy devices. Because many or most communicationdevices currently used are legacy devices, service providers will beable to offer IMS services to many more potential subscribers. Also,users that are comfortable with traditional telephones will have accessto IMS services without having to use an IMS-compatible device, and willstill be able to access the traditional services.

FIGS. 5-9 illustrate particular examples of how a call would be handledby a communication network according to the invention.

FIG. 5 illustrates a call flow in a communication network 500 in anexemplary embodiment of the invention. Communication network 500includes switching systems 510 and 570, IP network 520, calling partynetwork 530, called party network 550, and telephone numbering mapping(ENUM)/domain name server (DNS) database 540. Switching systems 510 and570 may comprise Lucent Softswitches (LSS) or another type of switches.Calling party network 530 includes a Proxy-Call Server Control Function(P-CSCF) 531, a Serving-CSCF (S-CSCF) 532, a Home Subscriber Server(HSS) 534, and one or more Application Servers (AS) 536. Called partynetwork 550 includes an Interrogate-CSCF (I-CSCF) 553, an S-CSCF 552, aP-CSCF 551, an HSS 554, and one or more Application Servers (AS) 556.Communication network 500 may include other systems, servers, andnetworks not shown in FIG. 5.

For this embodiment, a calling party 501 (through a legacy device 502)is placing a call to a called party 503 (through a legacy device 504).Assume that both calling party 501 and called party 503 are IMSsubscribers using legacy devices. Calling party 501 dials a numberthrough legacy device 502 for called party 503 to place a call incommunication network 500. Switching system 510 receives the call fromlegacy device 502 (arrow 571). Switching system 510 accesses subscriberdatabase (SUB DB) 511 to determine whether calling party 501 is an IMSsubscriber. Subscriber database 511 is pre-provisioned with identitiesof IMS subscribers, such as telephone numbers or URLs. For eachidentity, subscriber database 511 also includes an IMS field indicatingwhether that party is an IMS subscriber. If the IMS field is set to“true”, then the party is an IMS subscriber. If the IMS field is set to“false”, then the party is not an IMS subscriber. Calling party 501 isan IMS subscriber in this embodiment, so switching system 510 determinesthat calling party 501 is an IMS subscriber. Switching system 510 alsodetermines whether called party 503 is an IMS subscriber.

Switching system 510 then routes the call to P-CSCF 531 over IP network520 by transmitting a SIP INVITE message to P-CSCF 531 (arrow 572).Switching system 510 includes or inserts an indicator in the header ofthe SIP INVITE message that calling party 501 is an IMS subscriber. Anew field may be added to the INVITE message to accommodate theindicator. Switching system 510 also includes an indicator in the headerthat called party 503 is an IMS subscriber.

When P-CSCF 531 receives the INVITE message, P-CSCF 531 checks theINVITE message header to determine if calling party 501 is an IMSsubscriber. Because the indicator in the header indicates that callingparty 501 is an IMS subscriber, P-CSCF 531 checks if there is a mappingexisting for calling party 501 to route the call to the related S-CSCF532. If no mapping exists, P-CSCF 531 queries HSS 534 with a LocationInformation Request (LIR) with a number for calling party 501 (arrow573). HSS 534 processes the LIR and determines that S-CSCF 532 will beserving the call. The S-CSCF's are pre-provisioned in HSS 534 for IMSsubscribers using legacy devices. HSS 534 selects S-CSCF 532 based onthe number for calling party 501, and transmits a Location InformationAnswer (LIA) to P-CSCF 531 with the information on S-CSCF 532 (arrow574). P-CSCF 531 enters the number for calling party 501 and theinformation on S-CSCF 532 for calling party 501 into a mapping table(not shown). P-CSCF 531 retrieves the address of S-CSCF 532 from themapping table, and transmits the INVITE message to S-CSCF 532 (arrow575).

S-CSCF 532 checks the INVITE message header to determine if callingparty 501 is an IMS subscriber. Because the indicator in the headerindicates that calling party 501 is an IMS subscriber, S-CSCF 532determines if a service profile for calling party 501 is alreadydownloaded from HSS 534. If the service profile is not alreadydownloaded, S-CSCF 532 transmits a service assignment request (SAR) forthe service profile to HSS 534 (arrow 576). HSS 534 identifies theservice profile for calling party 501, and transmits a serviceassignment answer (SAA) to S-CSCF 532 that includes the service profilefor calling party 501 (arrow 577). S-CSCF 532 may store the serviceprofile for calling party 501 locally. For performance consideration,the service profile may be kept for a while and if no more calls aremade from the same calling party 501 after a pre-defined period of time,S-CSCF 532 will clear the service profile and download the data again ifa new call is made from calling party 501.

S-CSCF 532 analyzes the service profile of calling party 501 anddetermines whether to trigger AS 536. If S-CSCF 532 determines that AS536 is to be triggered, then S-CSCF 532 transmits the INVITE message toAS 536 (arrow 578). AS 536 checks the service of calling party 501 andtransmits the INVITE message back to S-CSCF 532 (arrow 579). When AS 536transmits the INVITE message back to S-CSCF 532, S-CSCF 532 may takethree possible options to transmit the INVITE message to called partynetwork 550.

First, S-CSCF 532 may query ENUM/DNS database 540 with the number ofcalled party 503 to get a URL for called party 503. S-CSCF 532 may thendetermine the address of I-CSCF 553 based on the URL for called party503. S-CSCF 532 can then transmit the INVITE message to I-CSCF 553 basedon the determined address.

Second, if the number of called party 503 is an E164 number and S-CSCF532 cannot get the URL for called party 503, then S-CSCF 532 may routethe INVITE message to a Break out Gateway Control Function (BGCF) (notshown). The BGCF may then route the INVITE message to I-CSCF 553 basedon a routing table provisioned for the BGCF.

Third, S-CSCF 532 may directly transmit the INVITE message to apre-arranged I-CSCF 553.

Responsive to receiving the INVITE message (arrow 580), I-CSCF 553transmits an LIR for called party 503 to HSS 554 (arrow 581). Becausecalled party 503 is also an IMS subscriber, an S-CSCF 552 ispre-provisioned in HSS 554 for called party 503. HSS 554 processes theLIR and determines the S-CSCF 552 for called party 503. HSS 554transmits a LIA to I-CSCF 553 with the information on S-CSCF 552 (arrow582). I-CSCF 553 then transmits the INVITE message to S-CSCF 552 (arrow583).

S-CSCF 552 receives the INVITE message and checks the INVITE messageheader to determine if called party 503 is an IMS subscriber. Becausethe indicator in the header indicates that called party 503 is an IMSsubscriber, S-CSCF 552 determines if a service profile already existsfor called party 503. If the service profile is not already downloaded,S-CSCF 552 transmits a SAR for the service profile to HSS 554 (arrow584). HSS 554 identifies the service profile for called party 503, andtransmits an SAA to S-CSCF 552 that includes the service profile forcalled party 503 (arrow 585). S-CSCF 552 may store the service profilefor called party 503 locally. For performance consideration, the serviceprofile may be kept for a while and if no more calls are made to thesame called party 503 after a pre-defined period of time, S-CSCF 552will clear the service profile and download the data again if a new callis made to called party 503.

S-CSCF 552 analyzes the service profile of called party 503 anddetermines whether to trigger AS 556. If S-CSCF 552 determines that AS556 is to be triggered, then S-CSCF 552 transmits the INVITE message toAS 556 (arrow 586). AS 556 checks the service of called party 503 andtransmits the INVITE message back to S-CSCF 552 (arrow 587). S-CSCF 552then transmits the INVITE message to P-CSCF 551 (arrow 588).

P-CSCF 551 enters S-CSCF 552 and called party 503 into its mapping table(not shown) if not yet existing. P-CSCF 551 then transmits the SIPINVITE message to switching system 570 through IP network 520 (arrow589). Switching system 570 then routes the call to legacy device 504(arrow 590). The subsequent call flow follows the standard IMS callflow.

FIG. 6 illustrates another call flow in communication network 500 in anexemplary embodiment of the invention. In this embodiment, calling party501 (through legacy device 502) is placing a call to a called party 605(through an IMS device 606). Assume again that both calling party 501and called party 605 are IMS subscribers, but called party 605 is usingan IMS-compliant device instead of a legacy device as in FIG. 5. Thesame process occurs as described above until S-CSCF 552 receives the SIPINVITE message (arrows 571-583). When S-CSCF 552 receives the INVITEmessage, S-CSCF 552 checks the INVITE message header to determine ifcalled party 605 is an IMS subscriber. In this case, called party 605 isan IMS subscriber, so S-CSCF 552 uses the service profile that wasalready downloaded from HSS 554 during registration of called party 605.S-CSCF 552 analyzes the service profile of called party 605 anddetermines whether to trigger AS 556. If S-CSCF 552 determines that AS556 is needed, then S-CSCF 552 transmits the INVITE message to AS 556(arrow 684). AS 556 checks the terminating service of called party 605,and returns a proper message to S-CSCF 552 (arrow 685). S-CSCF 552 thentransmits the INVITE message to P-CSCF 551 (arrow 686).

P-CSCF 551 then transmits the SIP INVITE message to switching system 570through IP network 520 (arrow 687). Switching system 570 then routes thecall to IMS device 606 (arrow 688). The subsequent call flow follows thestandard IMS call flow.

FIG. 7 illustrates another call flow for communication network 500 in anexemplary embodiment of the invention. For this embodiment,communication network 500 further includes a Break out Gateway ControlFunction (BGCF) 752, a Media Gateway Control Function (MGCF) 754, and aPSTN 756.

Calling party 501 (through legacy device 502) is placing a call to acalled party 703 (through a PSTN device 704). Assume that calling party501 is an IMS subscriber and called party 703 is not an IMS subscriberbut is a traditional PSTN subscriber. The same process occurs asdescribed in FIG. 5 until S-CSCF 552 queries ENUM/DNS database 540 withthe E164 number of called party 703 to get the URL address of calledparty 703 (arrows 571-579). S-CSCF 552 queries ENUM/DNS database 540with the E164 number of called party 703 to get the URL address ofcalled party 703. In this case, the PSTN number of called party 703 doesnot have an associated URL. Therefore, S-CSCF 532 determines that thecall should be terminated to PSTN 756. S-CSCF 532 then transmits theINVITE message to BGCF 752 (arrow 780). BGCF 752 transmits the INVITEmessage to an available MGCF 754 based on a provisioned routing table(arrow 781). MGCF 754 performs any protocol conversion, and routes thecall to PSTN 756 based on a routing table (arrow 782). PSTN 765 routesthe call to PSTN device 704 (arrow 783).

FIG. 8 illustrates another call flow for communication network 500 in anexemplary embodiment of the invention. For this embodiment, AS 536initiates a call to called party 801 through legacy device 802. Assumethat called party 801 is an IMS subscriber.

AS 536 queries HSS 534 to get the identity of the S-CSCF 532 responsiblefor called party 801 (arrow 871). HSS 534 determines the S-CSCF 532 forcalled party 801 and transmits information on S-CSCF 532 to AS 536(arrow 872). AS 536 transmits a SIP INVITE message to S-CSCF 532 (arrow873). AS 536 includes an indicator in the header of the INVITE messagethat called party 801 is an IMS subscriber. When S-CSCF 532 receives theINVITE message from AS 536, S-CSCF 532 checks the header to determine ifcalled party 801 is an IMS subscriber. Because the indicator in theheader indicates that called party 801 is an IMS subscriber, S-CSCF 532determines if a service profile for called party 801 is alreadydownloaded from HSS 534. If the service profile is not alreadydownloaded, S-CSCF 532 transmits an SAR for the service profile to HSS534 (arrow 874). HSS 534 identifies the service profile for called party801, and transmits an SAA to S-CSCF 532 that includes the serviceprofile for called party 801 (arrow 875). S-CSCF 532 may store theservice profile for called party 801 locally. For performanceconsideration, the service profile may be kept for a while and if nomore calls are made to the same called party 801 after a pre-definedperiod of time, S-CSCF 532 will clear the service profile and downloadthe data again if a new call is made to called party 801.

S-CSCF 532 analyzes the service profile of called party 801 anddetermines whether to trigger AS 536. If S-CSCF 532 determines that AS536 is needed, then S-CSCF 532 transmits the INVITE message to AS 536(arrow 876). AS 536 checks the service of called party 801 and transmitsthe INVITE message back to S-CSCF 532 (arrow 877).

S-CSCF 532 then routes the INVITE message to P-CSCF 531 (arrow 878).P-CSCF 531 then transmits the INVITE message to switching system 510through IP network 520 (arrow 879). Switching system 510 routes the callto legacy device 802 (arrow 880). The subsequent call flow follows thestandard IMS call flow.

FIG. 9 illustrates another call flow for communication network 500 in anexemplary embodiment of the invention. For this embodiment, a callingparty 901 makes an unauthorized call through a legacy device 902, andthe call is rejected by P-CSCF 531. Assume that calling party 901 is anIMS subscriber.

Calling party 901 dials a number through legacy device 902 to place acall in communication network 500. Switching system 510 receives thecall from legacy device 902 (arrow 971). Switching system 510 accessessubscriber database 511 to determine whether calling party 901 is an IMSsubscriber. Because switching system 510 determines that calling party901 is an IMS subscriber, switching system 510 routes the call to P-CSCF531 over IP network 520 by transmitting a SIP INVITE message to P-CSCF531 (arrow 972). Switching system 510 includes an indicator in theheader of the SIP INVITE message that calling party 901 is an IMSsubscriber. A new field may be added to the INVITE message toaccommodate the indicator.

When P-CSCF 531 receives the INVITE message, P-CSCF 531 checks theINVITE message header to determine if calling party 901 is an IMSsubscriber. Because the indicator in the header indicates that callingparty 901 is an IMS subscriber, P-CSCF 531 checks if there is a mappingexisting for calling party 901 to route the call to the related S-CSCF532. If no mapping exists, P-CSCF 531 queries HSS 534 with an LIR with anumber for calling party 901 (arrow 973). P-CSCF 531 receives an LIAfrom HSS 534 (arrow 974). P-CSCF 531 checks the LIA to see if the callshould be rejected (e.g., there is no S-CSCF provisioned for callingparty 901, or HSS 534 returned an error message). P-CSCF 531 transmitsthe proper SIP message to switching system 510 to reject the call (arrow975). Switching system 510 transmits this message to legacy device 902with the proper signaling (arrow 976).

FIG. 10 illustrates switching system 510 in an exemplary embodiment ofthe invention. One example of switching system 510 is a LucentSoftswitch (LSS). Switching system 510 includes an originating interface(I/F) 1002 having a device server (DS) 1004 and a call server (CS) 1006for the originating end point. The originating interface 1002 alsoincludes a call server (CS) 1008 and a SIP device server (SIP DS) 1010for the application servers. Switching system 510 also includes aterminating interface 1012 having a SIP device server (SIP DS) 1014 anda call server (CS) 1016 for the application servers. The terminatinginterface 1012 also includes a call server (CS) 1018 and a device server(DS) 1020 for the terminating end point. Switching system 510 furtherincludes subscriber database 511, and a SIP server 1030. SIP server 1030communicates with HSS 534 and AS 536 (see FIG. 5). SIP server 1030includes the functionality for a P-CSCF, an S-CSCF, an I-CSCF, a BGCF,etc.

When an IMS subscriber places a call, switching system 510 receives thecall through device server 1004. Call server 1006 accesses thesubscriber database 511 to determine if calling party is an IMSsubscriber. If the calling party is not an IMS subscriber, then callserver 1006 routes the call normally as a wire line call withoutinvoking SIP server 1030 and AS 536. If the calling party is an IMSsubscriber, then call server 1006 routes the call to SIP server 1030 viaSIP device server 1010.

SIP server 1030 runs the CSCF functionality, queries HSS 534 for aservice profile of the calling party, invokes AS 536, and routes thecall to SIP device server 1014 via either the P-CSCF (when the calledparty is another IMS subscriber) or the BGCF (when the called party is aPSTN subscriber).

1. A system, comprising: a switching system that serves a legacy devicewhich is not able to register with an IP Multimedia Subsystem (IMS)network, wherein the switching system is within a circuit-switchedlegacy network and outside of the IMS network; the switching systemreceives a call from a calling party using the legacy device to a calledparty, and determines where to route the call based on whether thecalling party is an IMS subscriber using a legacy device; if the callingparty is an IMS subscriber using a legacy device, then the switchingsystem routes signaling for the call to the IMS network so that thecalling party is able to access IMS services through the legacy deviceeven though the legacy device does not perform IMS registration; and ifthe calling party is not an IMS subscriber using a legacy device, thenthe switching system routes the signaling for the call to a non-IMSnetwork.
 2. The system of claim 1 further comprising: a subscriberdatabase that stores identities of IMS subscribers that use legacydevices which are not able to register with the IMS network.
 3. Thesystem of claim 2 wherein: the switching system determines an identifierfor the calling party, and accesses the subscriber database based on thecalling party identifier to determine if the calling party is an IMSsubscriber using a legacy device.
 4. The system of claim 2 wherein thesubscriber database is pre-provisioned with the identities indicatingwhether IMS subscribers are using legacy devices.
 5. The system of claim1 wherein the switching system, in order to route the call to the IMSnetwork, generates a packet signaling message for the call, includes anindicator in a header of the packet signaling message that the callingparty is an IMS subscriber, and transmits the packet signaling messageto the IMS network.
 6. The system of claim 5 wherein the IMS networkprocesses the indicator in the header of the packet signaling message toidentify a service profile for the calling party and to identify aserving-call session control function (CSCF) for the call.
 7. The systemof claim 5 wherein the packet signaling message comprises a SessionInitiation Protocol (SIP) message.
 8. The system of claim 1 wherein theIMS network determines if the called party is an IMS subscriber, androutes the signaling for the call to a non-IMS network if the calledparty is not an IMS subscriber.
 9. The system of claim 8 wherein the IMSnetwork routes the signaling for the call to a call session controlfunction (CSCF) for the called party if the called party is an IMSsubscriber.
 10. A method of operating a communication network forproviding a legacy device access to an IP Multimedia Subsystem (IMS)network, the method comprising: receiving a call from a calling partyusing a legacy device to a called party into a switching system, whereinthe switching system is within a circuit-switched legacy network andoutside of the IMS network; determining where to route the call based onwhether the calling party is an IMS subscriber using a legacy devicerouting the signaling for the call from the switching system to the IMSnetwork if the calling party is an IMS subscriber using a legacy deviceso that the calling party is able to access IMS services through thelegacy device even though the legacy device does not perform IMSregistration; and routing the signaling for the call from the switchingsystem to a non-IMS network if the calling party is not an IMSsubscriber using a legacy device.
 11. The method of claim 10 furthercomprising: storing, in a subscriber database, identities of IMSsubscribers that use legacy devices which are not able to register withthe IMS network.
 12. The method of claim 11 further comprising:determining an identifier for the calling party; and accessing thesubscriber database based on the calling party identifier to determineif the calling party is an IMS subscriber using a legacy device.
 13. Themethod of claim 11 further comprising: pre-provisioning the subscriberdatabase with the identities indicating whether IMS subscribers areusing legacy devices.
 14. The method of claim 10 wherein routing thesignaling for the call from the switching system to the IMS networkcomprises: generating a packet signaling message for the call; includingan indicator in a header of the packet signaling message that thecalling party is an IMS subscriber; and transmitting the packetsignaling message from the switching system to the IMS network.
 15. Themethod of claim 14 further comprising: processing the indicator in theheader of the packet signaling message in the IMS network to identify aservice profile for the calling party and to identify a serving-callsession control function (CSCF) for the call.
 16. The method of claim 10further comprising: determining in the IMS network if the called partyis an IMS subscriber, and routing the signaling for the call from theIMS network to a non-IMS network if the called party is not an IMSsubscriber.
 17. The method of claim 16 further comprising: routing thesignaling for the call from the IMS network to a call session controlfunction (CSCF) for the called party if the called party is an IMSsubscriber.
 18. A communication network, comprising: a calling party IPMultimedia Subsystem (IMS) network; a subscriber database that storesidentities of IMS subscribers that use legacy devices which are not ableto register with the IMS network; and a switching system that serves alegacy device which is not able to register with the calling party IMSnetwork, wherein the switching system is within a circuit-switchedlegacy network and outside of the IMS network; the switching systemreceives a call from a calling party using the legacy device to a calledparty, accesses the subscriber database based on a calling partyidentifier to determine where to route the call based on whether thecalling party is an IMS subscriber using a legacy device, routessignaling for the call to the calling party IMS network if the callingparty is an IMS subscriber using a legacy device so that the callingparty is able to access IMS services even though the legacy device doesnot perform IMS registration, and routes the signaling for the call to anon-IMS network if the calling party is not an IMS subscriber; thecalling party IMS network receives the call, determines if the calledparty is an IMS subscriber, and routes the signaling for the call to thenon-IMS network if the called party is not an IMS subscriber.
 19. Thecommunication network of claim 18 wherein the calling party IMS networkroutes the signaling for the call to a Break out Gateway ControlFunction (BGCF) if the called party is not an IMS subscriber.
 20. Thecommunication network of claim 18 wherein the calling party IMS networkroutes the signaling for the call to a called party IMS network if thecalled party is an IMS subscriber.